The detection of physiological activity at the microscopic level is key for understanding the function of biosystems and relating this to their physical structure. Current sensing methods for in vitro study of living tissue often rely on invasive probes to stimulate and detect activity, bearing the risk of inducing damage in the target system. In recent years, a new type of quantum sensor based on color centers in diamond has begun to offer the possibility to instead passively sense and image living biological systems. Here, we use such a sensor to realize the recording of the biomagnetic field generated by tightly focused, high intensity pulsed laser optogenetic neuromuscular stimulation of extensor digitorum longus muscles, dissected from mice and kept alive in carbogenated solution. Recordings captured a compound action potential response and a slow signal component, which we seek to explain using a detailed model of the biological system. We show proof-of-principle experimental recording of localized neuromuscular activity from the laser stimulation site without photovoltaic or fluorescence artifacts associated with alternative techniques. Our work represents a further step toward passive sensing and imaging at the microscopic level with quantum sensing, enabling further research into mapping of neural activity and intracellular processes.